US20040190003A1 - Interferometric method and system - Google Patents
Interferometric method and system Download PDFInfo
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- US20040190003A1 US20040190003A1 US10/806,593 US80659304A US2004190003A1 US 20040190003 A1 US20040190003 A1 US 20040190003A1 US 80659304 A US80659304 A US 80659304A US 2004190003 A1 US2004190003 A1 US 2004190003A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02055—Reduction or prevention of errors; Testing; Calibration
- G01B9/0207—Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
- G01B11/0608—Height gauges
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
- G01B9/02017—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations
- G01B9/02019—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations contacting different points on same face of object
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
- G01B2290/70—Using polarization in the interferometer
Definitions
- the present invention relates to the field of interferometric measuring methods, for applications such as profile measurements, roughness measurements, plainness measurements, and measurements of the radius of curvature as well as to an arrangement for implementing this method.
- Interferometers are being increasingly used in a number of production processes to characterize and measure surfaces.
- Optical measuring devices of this kind are distinguished by a high degree of measuring accuracy. For manufacturing, it is desirable to make measurements without contacting the measured part to avoid damage. It is also desirable that measurements be fully automated.
- a measuring device of this kind is the Laser Spot Scanning Interferometer (LASSI) described in U.S. Pat. No. 4,298,283 assigned to the assignee of the present invention, incorporated herein by reference.
- the underlying measuring principle is based on scanning the surface to be tested with two laser light beams which are simultaneously focused adjacent to each other onto the surface. During this process, the optical phase difference between the two light waves, which are reflected from the surface, changes linearly as a function of the height difference between the two laser spots on the surface. The phase difference is determined by phase shifting.
- an electro-optical light modulator is used which periodically shifts the phase difference between the two light waves by a fixed amount. At the same time, the intensity of the two interfering light beams is measured by a photodiode.
- the orthogonally polarized light beams with the phase difference are initially split by a beam splitter into several partial beam pairs, which, by means of a lens, are focused as parallel beams into a phase shifter, a polarizer, and an array of light sensors. Phase differences of the light beams create intensity differences between the beams received by the different light sensors. High measuring speed and accuracy are thus provided.
- the method and apparatus can be used to determine height differences along the surface.
- the present invention aims to provide an improved interferometric method and apparatus for enabling an increased precision of the interferometric measurement.
- the present invention provides an improved interferometric method, which eliminates the material-dependent phase shift from the total phase shift of the reflected return beams.
- This material-dependent phase shift which is also referred to as phase change on reflection (Fresnel phase shift) occurs when light is reflected from a dielectric or a metal and is dependent on the optical properties of the reflecting surface, in particular the index of refraction and the index of absorption and the optical properties of the ambient medium.
- the determination of the current material-dependent phase shift is performed based on a reflectivity measurement of the region on the reflecting surface onto which the measurement beam is directed.
- a reflectivity measurement of the region on the reflecting surface onto which the measurement beam is directed When the optical properties of the reference surface which reflects the reference beam is known, this facilitates determination of the material-dependent phase shift.
- both the measurement beam and the reference beam are reflected by the same surface.
- both the reflectivity of the region of the surface reflecting the measurement beam as well as the reflectivity of the surface region which reflects the reference beam need to be measured for the determination of the material-dependent phase shift.
- the fringe visibility value which is delivered by a phase analyzer, is used to further improve the precision of the calculation of the material-dependent phase shift.
- the present invention is particularly advantageous for measuring the topography of a surface which has a random distribution of areas having two different optical properties.
- An example for such a surface is AlTiC substrate (Al 2 O 3 —TiC) which of Al 2 O 3 in which TiC particles having randomly varying sizes and forms are embedded.
- AlTiC substrate is used for the production of storage disk read/write heads.
- the interferometric method of the invention can thus be advantageously employed for measuring the topography of the read/write head surface in the production of such heads and for quality monitoring.
- FIG. 1 shows a block diagram of an interferometric system
- FIG. 2 is illustrative of the random distribution of areas having different optical properties on the measurement surface
- FIG. 3 is a group of curves relating reflectivities to material-dependent phase shifts
- FIG. 4 is a curve relating the reflectivity of the measurement beam to the material-dependent phase shift.
- FIG. 1 shows interferometric system 100 having a laser 102 for generating laser beam 104 .
- Laser beam 104 passes through ⁇ 2-plate 106 and is polarised by linear polarizer 108 .
- the polarised laser beam 104 goes through beam splitter 110 and is divided into coherent light beams 112 and 114 by Wollaston-prism 116 .
- Orthogonally polarised light beams 112 and 114 pass through lens 118 , beam splitter 120 , lens 122 , and objective lens 126 before they are reflected from surface 128 to be measured.
- Light beam 112 is reflected from region 134 into return beam 130 .
- Light beam 114 is reflected from region 136 on surface 128 into return beam 132 .
- a portion 138 is divided from light beam 112 by beam splitter 120 and directed through optics 142 onto photo diode 144 .
- Photo diode 144 outputs a signal A which is proportional to the intensity of the light beam 112 .
- beam splitter 120 provides portion 140 of light beam 114 which is directed through optics 142 to photo diode 146 which outputs a signal B which is proportional to the intensity of light beam 114 .
- portion 172 of return beam 130 is provided by beam splitter 120 and directed through optics 150 to photo diode 152 .
- Photo diode 152 outputs signal C which is proportional to the intensity of return beam 130 .
- beam splitter 120 provides portion 148 of return beam 132 which is directed through optics 150 to photo diode 154 which provides signal D which is proportional to the intensity of return beam 132 .
- Wollaston-prism 116 and beam splitter 110 provide interference beam 158 which results from the interference of the return beams 130 and 132 to phase analyser 156 .
- Phase analyser 156 outputs a signal which is proportional to the total phase shift ⁇ T of return beams 130 and 132 . Further, phase analyser 156 provides signal V which is the fringe visibility.
- the signals A, B, C, D, ⁇ T and V are inputted into signal processing component 160 .
- ⁇ h the exact topography of the surface 128 can be determined.
- FIG. 2 shows a portion 162 of surface 128 (cf. FIG. 1).
- surface 128 belongs to a substrate which consists of a first material with embedded particles of a second material; the particles are randomly distributed and have random forms and shapes.
- the first material is Al 2 O 3 with embedded particles of TiC.
- Surface areas which are constituted by the first material are designated as a 1 and surface areas which are constituted by the second material are designated as a 2 in FIG. 2.
- Light beam 112 is directed on portion 162 which results in a circular illumination pattern 164 .
- Illumination pattern 164 covers a mixture of surface areas a 1 and a 2 .
- light beam 114 impinges on portion 166 of surface 128 which is also composed of surface areas a 1 and a 2 .
- Light beam 114 creates illumination pattern 168 on portion 166 .
- FIG. 3 shows the relationship between the reflectivity R 1 of the region on surface 128 which is covered by illumination pattern 164 ,the reflectivity R 2 of the region on surface 128 which is covered by illumination pattern 168 and the resulting material-dependent phase shift ⁇ m .
- the reflectivity R 1 is obtained by dividing signal C by signal A; likewise the reflectivity R 2 is obtained by dividing signal D by signal B (cf. FIG. 1, signal processing component 160 ).
- the material-dependent phase shift is determined and subtracted from the total phase shift ⁇ T which is provided by phase analyser 156 (cf. FIG. 1).
- the diagram of FIG. 3 can be obtained by a series of calibration measurements. Alternatively the diagram of FIG. 3 can be obtained by means of a mathematical model:
- ⁇ h topography-dependent_phase_shift
- ⁇ 1 phase_shift_caused_by_reflection_from_first_material
- ⁇ 2 phase_shift_caused_by_reflection_from_second_material
- R 1 reflectivity_of_first_region
- R 2 reflectivity_of_second_region
- ⁇ is a constant for a given pair of materials. This is because the reflection coefficient r 1 of the first material, the reflection coefficient r 2 of the second material as well as the material-dependent phase shift ⁇ 1 caused by reflection from the first material and the material-dependent phase shift ⁇ 2 caused by reflection from the second material are material constants. Thus ⁇ only needs to be calculated once for a given material pair which constitutes a surface and can be stored for future reference.
- light beam 112 serves as a measurement beam whereas light beam 114 serves as a reference light beam.
- light beam 114 is reflected from a reference surface having known optical properties.
- the reflectivity R 1 needs to be measured for the calculation of ⁇ and ⁇ m .
Abstract
The invention relates to an interferometric method for measuring a height of a first region on a first surface, the first surface having first areas having first optical properties and second areas having second optical properties, the method comprising the steps of generating of first and second coherent light beams, reflecting at least the first coherent light beam from the first region into a first return beam and reflecting the second coherent light beam from a second region into a second return beam, measuring at least a first reflectivity of the first region, determining a topography-dependent phase shift of the first and second return beams for the height measurement based on the first reflectivity.
Description
- This application claims priority to an application entitled “Interferometric Method and System” filed in the European Patent Office on Mar. 24, 2003, and assigned Application No. 03006539.5, the contents of which are hereby incorporated by reference.
- 1. Technical Field
- The present invention relates to the field of interferometric measuring methods, for applications such as profile measurements, roughness measurements, plainness measurements, and measurements of the radius of curvature as well as to an arrangement for implementing this method.
- 2. Description of the Related Art
- Interferometers are being increasingly used in a number of production processes to characterize and measure surfaces. Optical measuring devices of this kind are distinguished by a high degree of measuring accuracy. For manufacturing, it is desirable to make measurements without contacting the measured part to avoid damage. It is also desirable that measurements be fully automated.
- A measuring device of this kind is the Laser Spot Scanning Interferometer (LASSI) described in U.S. Pat. No. 4,298,283 assigned to the assignee of the present invention, incorporated herein by reference. The underlying measuring principle is based on scanning the surface to be tested with two laser light beams which are simultaneously focused adjacent to each other onto the surface. During this process, the optical phase difference between the two light waves, which are reflected from the surface, changes linearly as a function of the height difference between the two laser spots on the surface. The phase difference is determined by phase shifting. For this purpose, an electro-optical light modulator is used which periodically shifts the phase difference between the two light waves by a fixed amount. At the same time, the intensity of the two interfering light beams is measured by a photodiode.
- U.S. Pat. No. 5,392,116 which is assigned to the assignee of the present invention and is incorporated herein by reference, shows an interferometric phase measurement method, which permits simultaneous signal evaluation.
- The orthogonally polarized light beams with the phase difference are initially split by a beam splitter into several partial beam pairs, which, by means of a lens, are focused as parallel beams into a phase shifter, a polarizer, and an array of light sensors. Phase differences of the light beams create intensity differences between the beams received by the different light sensors. High measuring speed and accuracy are thus provided. When combined with means for directing two spatially separated orthogonally polarized beams on a surface, the method and apparatus can be used to determine height differences along the surface.
- The present invention aims to provide an improved interferometric method and apparatus for enabling an increased precision of the interferometric measurement.
- The present invention provides an improved interferometric method, which eliminates the material-dependent phase shift from the total phase shift of the reflected return beams. This material-dependent phase shift, which is also referred to as phase change on reflection (Fresnel phase shift), occurs when light is reflected from a dielectric or a metal and is dependent on the optical properties of the reflecting surface, in particular the index of refraction and the index of absorption and the optical properties of the ambient medium.
- When the measurement beam is moved over different areas of the reflecting surface having different optical properties the material-dependent phase shift changes correspondingly and thus introduces a measurement error. By measuring the actual material dependent phase shift for the region onto which the measurement beam is currently directed this measurement error is eliminated.
- The determination of the current material-dependent phase shift is performed based on a reflectivity measurement of the region on the reflecting surface onto which the measurement beam is directed. When the optical properties of the reference surface which reflects the reference beam is known, this facilitates determination of the material-dependent phase shift.
- In accordance with a preferred embodiment of the invention both the measurement beam and the reference beam are reflected by the same surface. In this instance both the reflectivity of the region of the surface reflecting the measurement beam as well as the reflectivity of the surface region which reflects the reference beam need to be measured for the determination of the material-dependent phase shift.
- In accordance with a further preferred embodiment of the invention the fringe visibility value, which is delivered by a phase analyzer, is used to further improve the precision of the calculation of the material-dependent phase shift.
- The present invention is particularly advantageous for measuring the topography of a surface which has a random distribution of areas having two different optical properties. An example for such a surface is AlTiC substrate (Al2O3—TiC) which of Al2O3 in which TiC particles having randomly varying sizes and forms are embedded. Such an AlTiC substrate is used for the production of storage disk read/write heads. The interferometric method of the invention can thus be advantageously employed for measuring the topography of the read/write head surface in the production of such heads and for quality monitoring.
- In the following text, preferred embodiments of the invention will be described in greater detail by making reference to the drawings in which:
- FIG. 1 shows a block diagram of an interferometric system,
- FIG. 2 is illustrative of the random distribution of areas having different optical properties on the measurement surface,
- FIG. 3 is a group of curves relating reflectivities to material-dependent phase shifts, and
- FIG. 4 is a curve relating the reflectivity of the measurement beam to the material-dependent phase shift.
- FIG. 1 shows
interferometric system 100 having alaser 102 for generatinglaser beam 104.Laser beam 104 passes through λ2-plate 106 and is polarised bylinear polarizer 108. The polarisedlaser beam 104 goes throughbeam splitter 110 and is divided intocoherent light beams prism 116. Orthogonally polarisedlight beams lens 118,beam splitter 120,lens 122, andobjective lens 126 before they are reflected fromsurface 128 to be measured.Light beam 112 is reflected fromregion 134 intoreturn beam 130.Light beam 114 is reflected fromregion 136 onsurface 128 intoreturn beam 132. - A
portion 138 is divided fromlight beam 112 bybeam splitter 120 and directed throughoptics 142 ontophoto diode 144.Photo diode 144 outputs a signal A which is proportional to the intensity of thelight beam 112. Likewisebeam splitter 120 providesportion 140 oflight beam 114 which is directed throughoptics 142 tophoto diode 146 which outputs a signal B which is proportional to the intensity oflight beam 114. - Further,
portion 172 ofreturn beam 130 is provided bybeam splitter 120 and directed through optics 150 tophoto diode 152.Photo diode 152 outputs signal C which is proportional to the intensity ofreturn beam 130. Likewisebeam splitter 120 providesportion 148 ofreturn beam 132 which is directed through optics 150 tophoto diode 154 which provides signal D which is proportional to the intensity ofreturn beam 132. - Wollaston-
prism 116 andbeam splitter 110 provideinterference beam 158 which results from the interference of thereturn beams phase analyser 156. Phase analyser 156 outputs a signal which is proportional to the total phase shift εΦT ofreturn beams phase analyser 156 provides signal V which is the fringe visibility. - The signals A, B, C, D, ΔΦT and V are inputted into
signal processing component 160. By means of the signals A, B, C, D and V,signal processing component 160 eliminates the material-dependent phase shift ΔΦm to provide the topography-dependent phase shift ΔΦh (ΔΦh=ΔΦT−ΔΦm). By means of ΔΦh the exact topography of thesurface 128 can be determined. - FIG. 2 shows a
portion 162 of surface 128 (cf. FIG. 1). In the example considered here surface 128 belongs to a substrate which consists of a first material with embedded particles of a second material; the particles are randomly distributed and have random forms and shapes. For example the first material is Al2 O3 with embedded particles of TiC. Surface areas which are constituted by the first material are designated as a1 and surface areas which are constituted by the second material are designated as a2 in FIG. 2. -
Light beam 112 is directed onportion 162 which results in acircular illumination pattern 164.Illumination pattern 164 covers a mixture of surface areas a1 and a2. - Likewise
light beam 114 impinges onportion 166 ofsurface 128 which is also composed of surface areas a1 and a2.Light beam 114 createsillumination pattern 168 onportion 166. - The average reflectivities of the regions covered by
illumination patterns - The diagram of FIG. 3 shows the relationship between the reflectivity R1 of the region on
surface 128 which is covered byillumination pattern 164,the reflectivity R2 of the region onsurface 128 which is covered byillumination pattern 168 and the resulting material-dependent phase shift ΔΦm. The reflectivity R1 is obtained by dividing signal C by signal A; likewise the reflectivity R2 is obtained by dividing signal D by signal B (cf. FIG. 1, signal processing component 160). With the R1 and R2 reflectivity values the material-dependent phase shift is determined and subtracted from the total phase shift ΔΦT which is provided by phase analyser 156 (cf. FIG. 1). - The diagram of FIG. 3 can be obtained by a series of calibration measurements. Alternatively the diagram of FIG. 3 can be obtained by means of a mathematical model:
- ΔΦh=ΔΦT−ΔΦm
- ΔΦm=arc sin(αβ)
-
- where
- ΔΦh: topography-dependent_phase_shift
- ΔΦT: total_phase_shift
- ΔΦm: material-dependent_phase_shift
- r1: reflection_coefficient_of materials_1
- r2: reflection_coefficient_of material_2
- Φ1: phase_shift_caused_by_reflection_from_first_material
- Φ2: phase_shift_caused_by_reflection_from_second_material
- R1: reflectivity_of_first_region
- R2: reflectivity_of_second_region
- V: fringe_visibility
- It is to be noted that α is a constant for a given pair of materials. This is because the reflection coefficient r1 of the first material, the reflection coefficient r2 of the second material as well as the material-dependent phase shift Φ1 caused by reflection from the first material and the material-dependent phase shift Φ2 caused by reflection from the second material are material constants. Thus α only needs to be calculated once for a given material pair which constitutes a surface and can be stored for future reference.
- The value of β needs to be recalculated for each position of the
illumination patterns - As is apparent from the above mathematical model ΔΦh=ΔΦT, if R1=R2. Hence, when R1=R2 the total phase shift does not require a correction. This enables one embodiment, where a height value is only outputted, when R1=R2 as in this instance no correction of the total phase difference is needed.
- Alternatively only
light beam 112 serves as a measurement beam whereaslight beam 114 serves as a reference light beam. In thisinstance light beam 114 is reflected from a reference surface having known optical properties. In this case only the reflectivity R1 needs to be measured for the calculation of β and ΔΦm. - This situation is illustrated in the diagram of FIG. 4 where the diagram of FIG. 3 is reduced to a
single curve 170 which relates the measured reflectivity R1 to the material-dependent phase shift ΔΦm. When theillumination pattern 164 oflight beam 112 covers a region which only consists of Al2O3 the additional phase shift ΔΦm is about 0 whereas whenillumination pattern 164 covers a region which only consists of TiC the phase shift ΔΦm is about 0.106 π which corresponds to a virtual height of about 16 nanometres for a measurement wavelength of 633 nanometers. This way a measurement error of up to 16 nanometers can be eliminated in the example considered here.
Claims (27)
1. An interferometric method for measuring, said method comprising:
generating a first coherent light beam and a second coherent light beam;
reflecting at least said first coherent light beam from a first region into a first return beam and reflecting said second coherent light beam from a second region into a second return beam;
measuring at least a first reflectivity of said first region;
determining a topography-dependent phase shift of said first return beam and said second return beam based on said first reflectivity; and
measuring a height based on said topography-dependent phase shift.
2. The method of claim 1 , further comprising:
comparing said first reflectivity and a second reflectivity of said second region; and
using a total phase shift of said first return beam and said second return beam for said height measurement, if said first reflectivity and said second reflectivity are equal.
3. The method of claim 1 , wherein said topography-dependent phase shift is determined based on an optical property of an area covered by said first region.
4. The method of claim 1 , wherein said determining step further comprises determining the topography-dependent phase shift with reference to a curve relating said first reflectivity to a material-dependent phase shift.
5. The method of claim 1 , wherein said determining step further comprises employing a reflectivity of a second region on a reference surface having known optical properties.
6. The method of claim 1 , wherein said determining step further comprises measuring a second reflectivity of a second region on said first surface; and
determining the topography-dependent phase shift based on said first reflectivity and said second reflectivity.
7. The method of claim 1 , wherein said determining step further comprises determining a fringe visibility for use in determining said topography-dependent phase shift.
8. The method of claim 1 , wherein said determining step further comprises determining a topography dependent phase shift through mathematical relationships, comprising:
ΔΦh=ΔΦT−ΔΦm;ΔΦm=arc sin(αrc;
wherein:
ΔΦh is a topography-dependent_phase_shift;
ΔΦT is a total_phase_shift;
ΔΦm is a material-dependent_phase_shift;
r1 is a reflection_coefficient_of_first_area;
r2 is a reflection_coefficient_of second_area;
Φ1 is a phase_shift_caused_by_reflection_from_first_area;
Φ2 is a phase_shift_caused_by_reflection_from_second_area;
R1 is a reflectivity_of_first_region;
R2 is a reflectivity_of_second_region; and
V is a fringe_visibility.
9. The method of claim 1 , wherein:
the determining step further comprises calculating a material-dependent phase shift based on a first optical property, a second optical property, and a first reflectivity of a first region; and
the determining step further comprises determining a topography-dependent phase shift by subtracting a material-dependent phase shift from a total phase shift of a first reflected coherent light beam and a second reflected coherent light beam.
10. A computer program product in a computer readable medium for measuring, said computer program product comprising:
a computer readable medium;
instructions on the computer readable medium for generating a first coherent light beam and a second coherent light beam;
instructions on the computer readable medium for reflecting at least said first coherent light beam from a first region into a first return beam and reflecting said second coherent light beam from a second region into a second return beam;
instructions on the computer readable medium for measuring at least a first reflectivity of said first region;
instructions on the computer readable medium for determining a topography-dependent phase shift of said first return beam and said second return beam based on said first reflectivity; and
instructions on the computer readable medium for measuring a height based on said topography-dependent phase shift.
11. The computer program product of claim 10 , further comprising:
instructions on the computer readable medium for comparing said first reflectivity and a second reflectivity of said second region; and
instructions on the computer readable medium for using a total phase shift of said first return beam and said second return beam for said height measurement, if said first reflectivity and said second reflectivity are equal.
12. The computer program product of claim 10 , wherein said instructions for determining said topography-dependent phase shift further comprise instructions for determining said topography-dependent phase shift based on an optical property of an area covered by said first region.
13. The computer program product of claim 10 , wherein said determining instructions further comprise instructions for determining the topography-dependent phase shift with reference to a curve relating said first reflectivity to a material-dependent phase shift.
14. The computer program product of claim 10 , wherein said determining instructions further comprise instructions for employing a reflectivity of a second region on a reference surface having known optical properties.
15. The computer program product of claim 10 , wherein said determining instructions further comprise:
instructions for measuring a second reflectivity of a second region on said first surface; and
instructions on the computer readable medium for determining the topography-dependent phase shift based on said first reflectivity and said second reflectivity.
16. The computer program product of claim 10 , wherein said determining instructions further comprise instructions for determining a fringe visibility for use in determining said topography-dependent phase shift.
17. The computer program product of claim 10 , wherein said determining instructions further comprise instructions for determining a topography dependent phase shift through mathematical relationships, comprising:
ΔΦh=ΔΦT−ΔΦm;ΔΦm=arc sin(αrc;
wherein:
ΔΦh is a topography-dependent_phase_shift;
ΔΦT is a total_phase_shift;
ΔΦm is a material-dependent_phase_shift;
r1 is a reflection_coefficient_of_first_area;
r2 is a reflection_coefficient_of_second_area;
Φ1 is a phase_shift_caused_by_reflection_from_first_area;
Φ2 is a phase_shift_caused_by_reflection_from_second_area;
R1 is a reflectivity_of_first_region;
R2 is a reflectivity_of_second_region; and
V is a fringe_visibility.
18. The computer program product of claim 10 , wherein:
the determining instructions further comprise instructions for calculating a material-dependent phase shift based on a first optical property, a second optical property, and a first reflectivity of a first region; and
the determining instructions further comprise instructions for determining a topography-dependent phase shift by subtracting a material-dependent phase shift from a total phase shift of a first reflected coherent light beam and a second reflected coherent light beam.
19. An interferometer for measuring height said interferometer comprising:
means for generating a first coherent light beam and a second coherent light beam;
means for reflecting at least said first coherent light beam from a first region into a first return beam and reflecting said second coherent light beam from a second region into a second return beam;
means for measuring at least a first reflectivity of said first region;
means for determining a topography-dependent phase shift of said first return beam and said second return beam based on said first reflectivity; and
means for measuring a height based on said topography-dependent phase shift.
20. The interferometer of claim 19 , further comprising:
means for comparing said first reflectivity and a second reflectivity of said second region; and
means for using a total phase shift of said first return beam and said second return beam for said height measurement, if said first reflectivity and said second reflectivity are equal.
21. The interferometer of claim 19 , wherein said means for determining said topography-dependent phase shift further comprise means for determining said topography-dependent phase shift based on an optical property of an area covered by said first region.
22. The interferometer of claim 19 , wherein said determining means further comprise means for determining said topography-dependent phase shift with reference to a curve relating said first reflectivity to a material-dependent phase shift.
23. The interferometer of claim 19 , wherein said determining means further comprise means for employing a reflectivity of a second region on a reference surface having known optical properties.
24. The interferometer of claim 19 , wherein said determining means further comprise means for measuring a second reflectivity of a second region on said first surface; and
means for determining the topography-dependent phase shift based on said first reflectivity and said second reflectivity.
25. The interferometer of claim 19 , wherein said determining means further comprise means for determining a fringe visibility for use in determining said topography-dependent phase shift.
26. The interferometer of claim 19 , wherein said determining means further comprise means for determining a topography dependent phase shift through mathematical relationships, comprising:
ΔΦh=ΔΦT−ΔΦm;ΔΦm=arc sin(αrc;
wherein:
ΔΦh is a topography-dependent_phase_shift;
ΔΦT is a total_phase_shift;
ΔΦm is a material-dependent_phase_shift;
r1 is a reflection_coefficient_of_first_area;
r2 is a reflection_coefficient_of_second_area;
Φ1 is a phase_shift_caused_by_reflection_from_first_area;
Φ2 is a phase_shift_caused_by_reflection_from_second_area;
R1 is a reflectivity_of_first_region;
R2 is a reflectivity_of_second_region; and
V is a fringe_visibility.
27. The interferometer of claim 19 , wherein:
the determining means further comprise means for calculating a material-dependent phase shift based on a first optical property, a second optical property, and a first reflectivity of a first region; and
the determining means further comprise means for determining a topography-dependent phase shift by subtracting a material-dependent phase shift from a total phase shift of a first reflected coherent light beam and a second reflected coherent light beam.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US11/481,101 US7397569B2 (en) | 2003-03-24 | 2006-07-05 | Method and system for interferometric height measurement |
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DE03006539.5 | 2003-03-24 | ||
EP03006539 | 2003-03-24 |
Related Child Applications (1)
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US11/481,101 Continuation US7397569B2 (en) | 2003-03-24 | 2006-07-05 | Method and system for interferometric height measurement |
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US11/481,101 Expired - Fee Related US7397569B2 (en) | 2003-03-24 | 2006-07-05 | Method and system for interferometric height measurement |
US12/059,001 Expired - Fee Related US7551291B2 (en) | 2003-03-24 | 2008-03-31 | Interferometric height measurement |
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US12/059,017 Expired - Fee Related US7551292B2 (en) | 2003-03-24 | 2008-03-31 | Interferometric Height Measurement |
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GB2516277A (en) * | 2013-07-17 | 2015-01-21 | Cambridge Consultants | Optical apparatus and methods |
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US7221459B2 (en) * | 2003-03-24 | 2007-05-22 | International Business Machines Corporation | Method and system for interferometric height measurement |
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US4298283A (en) * | 1978-11-30 | 1981-11-03 | International Business Machines Corporation | Interferometric measuring method |
US4844616A (en) * | 1988-05-31 | 1989-07-04 | International Business Machines Corporation | Interferometric dimensional measurement and defect detection method |
US5392116A (en) * | 1992-03-17 | 1995-02-21 | International Business Machines Corporation | Interferometric phase measurement |
US5604591A (en) * | 1994-04-11 | 1997-02-18 | Olympus Optical Co., Ltd. | Method of measuring phase difference and apparatus for carrying out the same |
US5914782A (en) * | 1996-08-08 | 1999-06-22 | Nikon Corporation | Differential polarization interference microscope for surface feature imaging |
US6580515B1 (en) * | 2001-05-29 | 2003-06-17 | Nanometrics Incorporated | Surface profiling using a differential interferometer |
US6856384B1 (en) * | 2001-12-13 | 2005-02-15 | Nanometrics Incorporated | Optical metrology system with combined interferometer and ellipsometer |
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JPH10293019A (en) * | 1997-04-18 | 1998-11-04 | Citizen Watch Co Ltd | Height shape measurement method and device using optical heterodyne interference |
US6295131B1 (en) * | 1998-02-20 | 2001-09-25 | Hitachi Electronics Engineering Co., Ltd. | Interference detecting system for use in interferometer |
US7221459B2 (en) * | 2003-03-24 | 2007-05-22 | International Business Machines Corporation | Method and system for interferometric height measurement |
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2004
- 2004-03-23 US US10/806,593 patent/US7221459B2/en not_active Expired - Fee Related
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2006
- 2006-07-05 US US11/481,101 patent/US7397569B2/en not_active Expired - Fee Related
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2008
- 2008-03-31 US US12/059,001 patent/US7551291B2/en not_active Expired - Fee Related
- 2008-03-31 US US12/059,017 patent/US7551292B2/en not_active Expired - Fee Related
Patent Citations (7)
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US4298283A (en) * | 1978-11-30 | 1981-11-03 | International Business Machines Corporation | Interferometric measuring method |
US4844616A (en) * | 1988-05-31 | 1989-07-04 | International Business Machines Corporation | Interferometric dimensional measurement and defect detection method |
US5392116A (en) * | 1992-03-17 | 1995-02-21 | International Business Machines Corporation | Interferometric phase measurement |
US5604591A (en) * | 1994-04-11 | 1997-02-18 | Olympus Optical Co., Ltd. | Method of measuring phase difference and apparatus for carrying out the same |
US5914782A (en) * | 1996-08-08 | 1999-06-22 | Nikon Corporation | Differential polarization interference microscope for surface feature imaging |
US6580515B1 (en) * | 2001-05-29 | 2003-06-17 | Nanometrics Incorporated | Surface profiling using a differential interferometer |
US6856384B1 (en) * | 2001-12-13 | 2005-02-15 | Nanometrics Incorporated | Optical metrology system with combined interferometer and ellipsometer |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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GB2516277A (en) * | 2013-07-17 | 2015-01-21 | Cambridge Consultants | Optical apparatus and methods |
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US7221459B2 (en) | 2007-05-22 |
US7551291B2 (en) | 2009-06-23 |
US7397569B2 (en) | 2008-07-08 |
US7551292B2 (en) | 2009-06-23 |
US20080180689A1 (en) | 2008-07-31 |
US20060250619A1 (en) | 2006-11-09 |
US20080180687A1 (en) | 2008-07-31 |
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